Temperature control system for jet convection strip heating furnace



D. BEGGs 3,186,694 TEMPERATURE CONTROL SYSTEM FOR JET CONVECTION June l, 1955 STRIP HEATING FURNACE Filed June 28, 1962 /lrm ATTY.

United States Patent 3,186,694 TEMERATURE CNTRL SYS'Elv FOR JET CNVESTUN STKE? EEA'HNG FURNACE Donald Boggs, Toledo, Ghia, assigner to Midland-Ross Corporation, Toledo, Unio, a corporation of hio Filed June 28, 1962, Ser. No. 205,901

4 Claims. (Cl. 263-3) Y This invention relates to a temperature control system for a furnace adapted to heat strip by convection heat transfer from free jets of compressible uid directed to impinge on alternate sides of the strip. The invention is particularly well suited for a thermal head strip heating furnace wherein the heating means for heating compressible fluid operates to heat compressible uid to a .temperature that is substantially higher than the temperature to which the strip is being heated.

ln the operation of a thermal head jet convection strip heating furnace it has been customary to control the heating effect of the compressible fluid heater in such a manner as to maintain the temperature of the compressible duid from the heater at a predetermined value. This was normally accomplished by means of a temperature control device responsive to a signal from a temperature sensing element, such as a thermocouple, disposed in the ductwork downstream of the heater, a location normally external to the furnace chamber.

It has now been discovered, however, that the temperature of the compressible fluid which actually impinges on the strip bears no iixed relationship to the temperature to which the heated compressible uid is heated by the heater. The reason for this phenomenon is that the jets of compressihle fluid which impinge on the strip do not consist solely of the heated compressible uid emitted toward the strip by the compressible fluid distributors, but rather, comprise a mixture of heated compressible iiuid and spent compressible fluid entrained by the heatedV compressible duid as it traverses the distance from the distributor toward the strip. ln a .typical installation the fluid which actually strikes the strip might comprise 70% of entrained spent fluid and only 30% heated fluid. Since the spent compressible fluid component of the heating jets comprises duid which has already transferred heat to strip it is at some lower temperature than the temperature of compressible iiuid from the heater. Furthermore, the difference between the temperature of the spent compressible r'luid portion of the heating 'et and the temperature of the heated compressible duid portion does not remain at a constant value since it is affected by the overall heating load of the furnace. The heating load of the furnace, in turn, is affected by the width of the strip being processed. Thus, in the operation of prior art jet convection thermal head strip heating furnaces, it is necessary to reset the control temperature to which the heater heats the com- Y pressible fluid to an empirically determined value every time the width of strip being processed is changed.

it is, therefore, the object of this invention to provide improved strip heating apparatus. It is a further object of the invention to provide an improved temperature control system for a thermal head jet convection strip heating furnace. it is a further object of the invention to provide such a temperature control system as to render the operation of the furnace insensitive to the width of the strip being processed.

F or a further consideration of what is considered to be novel and inventive, attention is directed to the following portionl of the specification, the drawing, and the appended claims.

in the drawing:

FiG. l is an etevational sectional view of strip treating apparatus having a heating section constructed in accordance with the present invention; and

ICC

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1.

As shown in FIG. l simplified apparatus for heat treating substantially endless moving strip 11 on a continuous basis comprises a heating duid collecting chamber 12, defined by insulated wall means 13, and a cooling chamber 14,illustrated schematically ybecause its details of construction do not constitute a part of this invention. Suitable strip conveying means comprising rollers 15 and 16 are provided to convey the strip through heating chamber 12 and cooling chamber 14 in that sequence.

Strip 11 is heated within chamber 12 by means of jets ofpcompressible uid which are directed against opposite sides thereof. Pursuant to this method of heating, circulating means comprising a blower 17 and a heater 13, illustrated schematically, are provided to circulate compressible fluid at a suitable temperature, usually at a temperature in excess of the desired final strip temperature, into the heating chamber. Heater 1S may be electrically heated, but is shown as being fuel fired and is provided with a fuel inlet line 19.v

The heated compressible uid from the circulating means is delivered to a manifold 21 from whence it passes, in parallel, into a first distributor 22 and a second distributor 23 spaced apart from the rst distributor. Each of the distributors is adapted to distribute the heated compressible fluid within the chamber in a plurality of jets having a component of motion directed toward the other of the distributors, and each comprises a generally vertically extending header 24 and a plurality of ported pipes 26-35 each of which is disposed in iiuid communication with the header and generally transversely thereof. The distributors are so arrangedV with respect to each other and with respect to the strip conveying means, which conveys the strip through the heating chamber intermediate the distributors, that the alternate sides of the strip are impinged upon by jets of compressible tiuid. After impingingon the strip and expending some of its heat thereby, the spent iiuid is collected in chamber 12 and may be evacuated therefrom and returned to blower 17 by means of conduit 41 to be recirculated back to the distributing means.

To control theheating effect of the heating jets of Compressible fluid on strip 11, temperature control means is provided to control the heatingeffect of heater 1S on the compressible fluid circulated therethrough. Appropriate control apparatus comprises a temperature sensing element 36, such as a thermocouple, located in a manner to be later discussed; an amplifier 37 adapted to receive a signalV from element 36 indicative of the temperature thereof and to transmit such signal at an amplified value; a controller 3S adapted to transmit a signal indicative of difference between the temperature sensed by element 36 and a predetermined set-point temperature; `and a ow control valve 39 subject to operation in response to the signal from controller 3S in such a manner as to increase the ow of fuel to heater 18 when the temperature sensed by element 36 is below the set point temperature and to decrease the flow of fuel when the temperature Vsensed Vby j element 36 is above the set point temperature.

The apparatus according to this invention differs from the prior art mainly in the location of thermalV sensing element 35. in the prior art it is customary to control the heating effect of the heater of a thermal head jet convection strip heating furnace in response to the temperature of a sensing element sensitive only to the temperature of compressible fluid from the heater, Yas by means of a thermocouple in the heated compressible fluid ductwork external to the'heating chamber. In .this invention, however, thermal sensing element 36 is located within heating chamber 12 intermediate distributors. Specifically, at least g i ported pipe from distributor 23 are provided with Vextended portions and thermal sensing elementis disposed in the region of convergence therefrom. In the illustrated arrangement, sensing element is disposed intermediate opposed ported extensions 23e of opposed ported pipes 28. y

The advantages of the present invention are grounded in the fact that thermal sensing element 36 is exposed heater t8 but also include lower temperature spent compressible iiuid entrained from the surroundings in chamber 12 by the jets of heated fluid from the ported pipes as they traverse the distance between the ports of the distributor and the strip. Thus, the temperature control system of thepresent invention automatically compensates for the eliect ofchange in the temperature of spent cooling fluid within chamber 12 as might be caused by a change in the width of strip being processed.

The best mode known to me to carry out this invention has been described in terms of sufciently full, clear,'con oise, and exact as to enable any person skilled in the art to practice the invention. However, it is understood that various modiications will be readily apparent to a skilled artisan without departing from the scope of the invention which is delined only by appended Claims.

I claim: Y

L'Heating apparatus comprising,kin combination: wall Vmeans defining a chamber; circulating means comprising a heater located externally of the chamber for circulating heated compressible iluid into the chamber; distributing means within thechamber ycomprising a first distributor and a second distributor spaced apart from the first distributor with each of the distributors being adapted'to receive Vheated compressible iiuid from the circulating means and to distribute heated compressible iuid vwithin the chamber in at least one free jet having a component of motion directed toward .the other of the distributors; means for disposing work in a normal location in the chamber intermediate the distributors and in such a manner as to be impinged upon on opposite sides by jets'comprising a mixture of heated compressible uid and spent compressible fluid from within the chamber; a temperature sensing element disposed within the chamber between the distribtuors and generally laterally aligned with the normal alemana location of the workin a manner to ybe impinged on by a mixture of compressible uid similar to the mixture impinging on thel work; and temperaturer control means sensitive to a condition indicative of the temperature of the temperature sensing element for controlling .the heating eiiect of the heater in a manner to maintain the temperature of the temperature sensing element atV a predetermined value.

2. Apparatus according to claim l wherein each of said first and second distributors comprises, in combination: a header; a plurality of ported pipes disposed transversely of the header and in uid communication therewith with f at least one .ported pipe from the first distributor and a a predetermined value.

d. In a heating method comprising heating compressible liuid and directing the heated compressible tiuid in opposed jets containing spent compressible fluid against opposite sides of the work being heated, the steps of sensing the temperature of the mixture of heated compressible iiuid and spent compressible iiuid in the region of coniverrgence of the opposed jets; and controlling the heating of compressible fluid to maintain the sensed temperature at a predetermined value.

References Cited by the Examiner "UNITED STATES PATENTS 2,406,822 9/46 Fox 263-8 2,897,096 9/57 Kullgren et al 34-45 2,862,305 12/58 Dungler 34-155 X 2,991,989 7/61 Martin 263-3 3,021,236 Y 2/62 Beggs et al 26S-3X 3,091,441 5/ 63 Kullgren et al 263-3 CHARLES SUKALO, Primary Examiner. toi-1N J. CAMBY, Examiner. 

1. IN A HEATING METHOD COMPRISING HEATING COMPRESSIBLE FLUID AND DIRECTING THE HEATED COMPRESSIBLE FLUID IN AT LEAST ONE FREE JET CONTAINING SPENT COMPRESSIBLE FLUID AGAINST THE WORK TO BE HEATED, THE STEPS OF SENSING THE TEMPERATURE OF THE MIXTURE OF HEATED COMPRESSIBLE FLUID AND ENTRAINED SPENT COMPRESSIBLE FLUID WHICH ACTUALLY IMPINGES ON THE WORK; AND CONTROLLING THE HEATING OF COMPRESSIBLE FLUID TO MAINTAIN THE SENSED TEMPERATURE AT A PREDETEMINED VALUE. 